Well I recently installed a CPU water-cooler on this system (more out of fun/whatever then for need), its a 2.01Ghz Athlon 64 CPU (Socket 754) now the BIOS reads the CPU at 34C idle, but SpeedFan reads the case (Sensor IT8712F it says) as being 34C, and the CPU (which it reads as AMD K8 Core) as being 27C, so which one is accurate? Also, originally what SpeedFan says is the CPU it use to idle at around 32C before I installed the water-cooling system, so is SpeedFan correct and is my bios reading off the motherboard sensor or what?

If you had read the disclaimer provided by the author on Speedfan page HERE, you would have figured by now that the mobo temperature reading (accessible via BIOS) is more realistic. i_Xp/VistaUser

The current temps in the bios have usually had slight adjustments made to them in the bios code such that the reading from the sensors on the mboard have a value automatically added or subtracted from them to reflect the actual temp found through testing for that sensor on that particular mboard, so they are usually more accurate. Generic mboard monitoring software usually doesn't have the information for specific mboards like that and can only go by the hardware monitoring chipset's specs. You may be able to make adjustments in SpeedFan, or other simlar generic software, to make the temps in Speedfan the same as those in the bios, best done when the system has fully warmed up and the temps are relatively stable. If SpeedFan can't do that, other generic software can - e.g. MBProbe, but it has not been updated since about 2002 and may not work for newer hardware monitoring chipsets (two download modules required for 2000/XP) Mboard manufacturers often have mboard monitoring software available that tends to be more accurate for their mboards, often on the CD that came with the mboard, and/or on their web site, often in the software downloads for your model, but you may not be able to make adjustments in them if the readings in the bios and the software are slightly different.

The temperature numbers themselves aren't really that important, as long as they are withing a reasonable range. Any significant change should be cause for investigation.